We report a novel use of cerebral oximetry in cardiac surgery using the Fore-Sight absolute cerebral oximeter (CAS Medical Systems Inc, Branford, CT). A patient with a persistent left superior vena cava underwent mitral and aortic valve replacement. We decided to tape and occlude the persistent left superior vena cava and used cerebral oximetry to compare left and right hemispheric oxygen saturation levels to ensure that cerebral perfusion was not impaired. The procedure was uneventful, and the patient was extubated 8 hours later without neurocognitive deficit.